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expert reaction to Britain’s Mammals 2018

The first comprehensive review of British mammal populations for more than 20 years has been launched by The Mammal Society and Natural England.


Dr Nathalie Pettorelli, Research Fellow at the Zoological Society of London, said

“It’s fantastic to see a comprehensive assessment of species’ current vulnerability to extinction our mammals – a lot of efforts went into this report, and the work clearly capitalises on the best available data for Great Britain.

“The results are however to be taken with a good pinch of salt: the general approach for estimating population size was to multiply habitat-specific density estimates by the extent of these habitats within the geographical range, using a classification of habitats derived from the land cover map for 2007 as a source of information for estimating the distribution of these habitats. As you can imagine, habitat distribution in Britain has changed a bit since 2007; mammals are unlikely to be evenly distributed in their habitats; and some species may be more generalist/more specialised than we think (i.e., we may think they are only found in a selection of known habitats, while they may in fact use a broader/narrower set of habitats). Our ability to detect mammals has also improved since the nineties: camera traps, which are known to facilitate the detection of shy and secretive species, were not commonly used to survey mammals twenty years ago. As mentioned in the report, the assessments presented in this review are ultimately based on very limited data and rely on various assumptions.

“That said, all these caveats are more likely to underestimate the number species at risk than overestimate it – and indeed, for most species assessed (52%) the population trend over the past 20 years is unknown. The reported decrease for hedgehogs, hazel dormouse, red squirrels, wild cats and water vole are very likely to be real and should be taken very seriously.

“One very strong message here is that there is a real need for more data on mammals in Britain, and for more regular assessments, if we want to be able to reliably detect problems before they can’t be fixed. The world’s biodiversity is now regularly assessed, with the living planet reports being published every 2 years and the global biodiversity outlook reports being published every 4-5 years. It’s incredible to think that no comprehensive assessment of the conservation status of mammals in Britain was published between 1995 and 2018.”


Prof Rob Smith, Emeritus Professor of Population Dynamics at the University of Huddersfield, said:

“It is notoriously difficult to estimate population sizes of mammals accurately, especially over large areas, and population estimates are generally very uncertain.  This Review of the Population and Conservation Status of British Mammals is, however, based on a comprehensive study commissioned by the English, Scottish and Welsh statutory conservation agencies that attempts to use consistent methodologies. The results should be taken seriously.

“Quite a lot of the news is glum, but by no means all of it. Almost one fifth of the 58 terrestrial species of mammal considered are reckoned to be at high risk of extinction. Species such as hedgehog and water vole that were common when I was growing up are seen much less frequently and may have declined by two thirds in 20 years.

“I did find room for optimism in the report in that the ranges of 18 species are reckoned to have increased over the last 20 years, compared with four that have decreased. Two of the 18, however, are reintroductions (beaver and wild boar) and seven others are non-native. Deer populations, both native and introduced species, seem to increase relentlessly.

“There is an assessment for each species of the drivers of population change, pressures faced and the likely reasons for increase or decrease. These assessments are not overstated and often include the usual suspects e.g. loss of habitat, changes in management of agricultural areas and waterways, use of pesticides.

“The authors are quite candid about uncertainties and data deficiencies, and they give a reliability index for each population estimate. For some species, expert opinion is the main guide. Nevertheless, this is a rigorous, thorough and timely assessment of the state of British mammals that is transparent in its methodology.

“The big picture to me is that estimated changes in mammal populations over the last 20 years do not indicate cause for concern overall although they do raise significant worries about particular species (wildcat, red squirrel, water vole and two of our bats). This is in contrast with other taxonomic groups such as butterflies and moths where concern about decline is more general.

“Much of the decline in biodiversity across Europe has been linked to agricultural intensification. Mammals and birds are specifically protected at an individual as well as population level under current pesticide legislation. They are therefore less likely than other groups to be adversely affected by direct effects of pesticides. In contrast, many non-target insects and plants are routinely eliminated by pesticide application in cropped fields, whether or not they are pests.”


Dr Vicky Wilkinson, Garden Wildlife Health Project Coordinator and Wildlife Veterinarian at ZSL said:

“The Mammal Society’s recent assessment of Britain’s hedgehog population provides further evidence that this well-loved species has suffered dramatic declines in recent decades. Garden Wildlife Health ( continue to work alongside The Mammal Society, and other organisations, to investigate whether infectious or non-infectious disease conditions could be an additional factor contributing to the species’ ongoing population decline.”


Dr Chris Carbone, Senior Research Fellow at the Institute of Zoology at ZSL said:

“The trends cited in this report make depressing reading, but also highlights the need for more widespread and reliable information on mammal distributions and population sizes, as there is a lot of uncertainty is these UK-wide estimates. ZSL has been working on methods to reliably estimate the distributions and population sizes of hedgehogs and other UK mammals in urban environments which are becoming increasingly important habitats for these species.”


Dr Scott Newey, animal ecologist at The James Hutton Institute, said:

“Mammals are an important part of our natural world. Though some species are well known and conspicuous, many are secretive and difficult to study. This report brings together the latest information and represents a much-needed update on population and conservation status of British mammals.”


* ‘Britain’s Mammals 2018’ published on Wednesday 13 June 2018.


Declared interests

Dr Newey contributed to the mountain and brown hare sections of the guide, and reviewed the mountain hare section, but is not an author.

Prof Smith: I am retired and do not have paid employment nor am I in receipt of any external funding. I have been an independent member and deputy chair of the UK Advisory Committee on Pesticides but this finished several years ago. I was an independent member of the UK Committee on Toxicity until last year. I have been an independent member of the European Food Safety Authority Panel on Plant Protection Products and their Residues for the last six years. All of my comments here are made in a personal capacity.

None others received.

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